: As said earlier, it takes a planetary sized network for an AI to go rampant.
: Durandal had the Marathon's network, which was huge. Now in order for
: Cortana to begin rampancy, she would need a huge network. That huge
: network would be the Forerunner's. Being in there for that long she
: undoubtedly had enough time to see every secret the Forerunner had.

: And another clue to Cortana not being so nice anymore. We all know how she
: already resents humans, especialy marines. She always underestimates them,
: presuming they are dead when they're not. And when she has to open the
: locked door aboard the T&R, she is mad because a marine told her to hurry
: up, and she says she would like to see him do that very quietly.

: Now if Cortana wanted to help MC stop the flood and 343 GS, why didn't she go
: with him to stop Keyes? She couldn't spare a few seconds for MC to pull
: her out of the core and back into MC? No doubt she could help him
: immensely with figuring out 343's true intentions. But could she get the
: index if she had gone with MC? I don't think so. She only got the index
: because 343 didn't know about her and he gave the index to MC to put into
: the core, and she intercepted it. So she stayed in the core to get the
: index.

: It is my opinion that the index holds more power than just activating Halo,
: and Cortana knew that before sending MC to stop Keyes. She knew it could
: help her with other motive she has.